Method for reforming a reflection-type light diffuser

Abstract

The invention provides a method for fabricating reflection-type light diffuser which is a substrate having a plurality of bumpy elements with reflective curved surfaces. Each of the plurality of bumpy elements having a first surface and a second surface, the first angle (alpha or theta) between the first surface and the substrate is different from the second angle (beta or phi) between the second surface and the substrate. A Multi-Exposure Shift Method along with specially designed masks are proposed for manufacturing the curved reflective elements in the present invention. The invention can also be used in a traditional TFT-LCD, with the diffusive film layer eliminated, as an element between the liquid crystal layer and the active matrix.

What is claimed is:  
     
       1. A method for fabricating reflection-type light diffuser, said reflection-type light diffuser being used for scattering incident light into a predetermined angular area away from specular ray, said method comprising: 
       forming a photoresist layer on a substrate;  
       using a first mask in a multi-exposure shift process to expose said photoresist layer, said multi-exposure shift process comprising:  
       using a first light source having a first power to expose said photoresist layer with said first mask positioned at a first position;  
       shifting said first mask by a pitch to a second position; and  
       using a second light source having a second power to expose said photoresist layer with said first mask positioned at a second position, said first power being unequal to said second power;  
       exposing said photoresist layer by using a second mask;  
       developing said photoresist layer to form a photoresist pattern, said photoresist pattern comprising a plurality of knob-on-slant structures parallel to each other, each of said plurality of knob-on-slant structures comprising a slant portion and a knob portion, said slant portion being resulted from said multi-exposure shift process using said first mask, said knob portion formed on said slant portion being resulted from said exposing step using said second mask, said slant portion comprising a first surface and a second surface, said first surface having a longer slant than said second surface, a first angle between said first surface and said substrate being unequal to a second angle between said second surface and said substrate; and  
       forming a reflective layer on said photoresist pattern, a normal direction of said first surface being pointing to a predetermined direction enabling reflective light of said incident light reflected by said reflective layer scattered into said predetermined angular area.  
     
     
       2. The method as claim  1  further comprising a baking process after said developing process, said baking process being used to smooth edges of said photoresist pattern. 
     
     
       3. The method as claim  1 , wherein a curve of said first surface in an incident plane including said incident light is monotonically convex. 
     
     
       4. The method as claim  1 , wherein the curve of said first surface in the incident plane including said incident light is monotonically concave. 
     
     
       5. The method as claim  1 , wherein each of said plurality of knob-on-slant structures having straight edges resulting form straight slits of said first mask. 
     
     
       6. The method as claim  1 , wherein each of said plurality of knob-on-slant structures having curved edges resulting form curve slits of said first mask. 
     
     
       7. A method for fabricating reflection-type light diffuser, said reflection-type light diffuser being used for scattering incident light into a predetermined angular area away from specular ray, said method comprising: 
       forming a photoresist layer on a substrate;  
       using an exposing step to expose said photoresist layer;  
       developing said exposed photoresist layer to form a photoresist pattern, said photoresist pattern comprising a plurality of stair structures parallel to each other, each of said plurality of stair structures comprising a first stair and a second stair, altitude of said first stair being higher than altitude of said second stair, said first stair being adjacent to said second stair; and  
       forming a reflective layer on said photoresist pattern, a normal direction of said first surface being pointing to a predetermined direction enabling reflective light of said incident light reflected by said reflective layer scattered into said predetermined angular area.  
     
     
       8. The method as claim  7  further comprising a baking process after said developing process, said baking process being used to smooth edges of said photoresist pattern. 
     
     
       9. The method as claim  7 , wherein said exposing step being a multi-exposure shift process, said multi-exposure shift process comprising: 
       using a first light source having a first power to expose said photoresist layer with a mask, said mask comprising a plurality of transparent slits, each of said plurality of transparent slits comprising a straight portion and a round arch portion;  
       shifting said mask by a pitch in both first direction and second direction, said first direction being parallel to said straight portion, said second direction being perpendicular to said first direction; and  
       using a second light source having a second power to expose said photoresist layer with said mask, said first power being unequal to said second power; and  
       shifting said mask by said pitch in both said first direction and said second direction.  
     
     
       10. The method as claim  7 , wherein said exposing step utilizes a light source to expose said photoresist layer under coverage of a mask, said mask comprising a first partial transparent area and a second partial transparent area, diaphaneity of said first partial transparent area being different from that of said second partial transparent area, said first stair of said stair structure being resulted from said exposure through said first partial transparent area. 
     
     
       11. A method for fabricating reflection-type light diffuser, said reflection-type light diffuser being used for scattering incident light into a predetermined angular area away from specular ray, said method comprising: 
       forming a photoresist layer on a substrate;  
       using an exposing step to expose said photoresist layer;  
       developing said photoresist layer to form a photoresist pattern, said photoresist pattern comprising a plurality of pumps, each of said pumps comprising a first flat portion and a second flat portion, altitude of said first flat portion being higher than altitude of said second flat portion, said first flat portion being adjacent to said second flat portion;  
       baking said developed photoresist pattern, edges of each of said pumps of said photoresist pattern being smoothed, each of said baked pumps comprising a first surface and a second surface, said first surface being longer than said second surface, a first angle between said first surface and said substrate being unequal to a second angle between said second surface and said substrate, said pumps being randomly distributed on said substrate; and  
       forming a reflective layer on said photoresist pattern, a normal direction of said first surface being pointing to a predetermined direction enabling reflective light of said incident light reflected by said reflective layer scattered into said predetermined angular area.  
     
     
       12. The method as claim  11 , wherein said exposing step being a multi-exposure shift process comprising: 
       using a first light source having a first power to expose said photoresist layer with a mask, said mask comprising a plurality of transparent regions;  
       shifting said mask by a pitch; and  
       using a second light source having a second power to expose said photoresist layer with said mask, said first power being unequal to said second power, said first flat portion of every of said pump being formed by exposing to said first light source, said second flat portion of every of said pump being formed by exposing to said second light source, said mask comprising a plurality of transparent regions that is distributed randomly, random distribution of said pumps being resulted from that of said transparent regions on said mask.  
     
     
       13. The method as claim  11 , wherein said exposing step utilizes a light source to expose said photoresist layer in one exposing step under coverage of a mask, said mask comprising a plurality of transparent regions, each of said transparent regions comprising a first partial transparent area and a second partial transparent area, diaphaneity of said first partial transparent area being different from that of said second partial transparent area, said first flat portion of every of said pumps being formed by exposing said photoresist pattern to said light source through said first partial transparent area, said second flat portion of every of said pumps being formed by exposing to said light source through said second partial transparent area, random distribution of said pumps being resulted from the random distribution of said transparent regions on said mask. 
     
     
       14. The method as claim  11 , wherein said exposing step being a multi-exposure process comprising: 
       using a first light source having a first power to expose said photoresist layer with a first mask at a position relative to said photoresist layer, said first mask comprising a first set of transparent regions; and  
       using a second light source having a second power to expose said photoresist layer with a second mask at said position relative to said photoresist layer, said second mask comprising a second set of transparent regions, area of said first set of transparent regions being greater than said second set of transparent regions, location of every of said first set of transparent regions being overlapped with said second set of transparent regions, said first power being unequal to said second power, said first flat portion of every of said pumps being formed by exposing to said first light source through said first mask, said second flat portion of every of said pump being formed by exposing to said second light source through said second mask.